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Acetylmethylenetriphenylphosphorane (12.91 g, 40.57 mmol) was dissolved in a mixture of diethyl ether (30 ml) and dichloromethane (10 ml) and stirred for 5 min, then 1,1,1-trifluoroacetone (5.00 g, 44.62 mmol) was added and the mixture was stirred at room temperature for 40 h. The precipitate formed was filtered off, the filter cake was washed with diethyl ether and the combined organic phases were concentrated cautiously under slightly reduced pressure. The crude solution of (3Z)-5,5,5-trifluoro-4-methylpent-3-en-2-one thus obtained was used without further purification in the next reaction step and taken up in toluene (25 ml). After the addition of ethyl acetoacetate (3.42 g, 26.29 mmol) and potassium tert-butoxide (0.88 g, 7.89 mmol), the resulting reaction mixture was stirred under reflux conditions for 5 h. After cooling to room temperature, water was added, the mixture was stirred vigorously for 5 minutes and then the aqueous phase was extracted repeatedly with dichloromethane. The combined organic phases were dried over magnesium sulfate, filtered and concentrated under reduced pressure. By final column chromatography purification of the resulting crude product (ethyl acetate/heptane gradient), it was possible to obtain 3,5-dimethyl-5-(trifluoromethyl)cyclohex-2-en-1-one (1.9 g, 38% of theory) in the form of a colorless oil. 3,5-Dimethyl-5-(trifluoromethyl)cyclohex-2-en-1-one (1.60 g, 8.33 mmol) was then dissolved in abs. toluene, and molybdatophosphoric acid hydrate (30 mg, 0.02 mmol), copper(II) sulfate pentahydrate (4 mg, 0.02 mmol) and molybdenum(VI) oxide (5 mg, 0.03 mmol) were added. The resulting reaction mixture was stirred with introduction of air under reflux conditions for 4 days. After cooling to room temperature, water was added, the mixture was stirred vigorously for 5 minutes and then the aqueous phase was extracted repeatedly with dichloromethane. The combined organic phases were dried over magnesium sulfate, filtered and concentrated under reduced pressure. By column chromatography purification of the resulting crude product (ethyl acetate/heptane gradient), it was possible to obtain 2,6-dimethyl-6-(trifluoromethyl)cyclohex-2-ene-1,4-dione (300 mg, 17% of theory) in the form of a colorless oil. 2,6-Dimethyl-6-(trifluoromethyl)cyclohex-2-ene-1,4-dione (520 mg, 2.52 mmol) was dissolved in 2,3-butanediol (4 ml) under argon, and trimethyl orthoformate (0.83 ml, 7.57 mmol) and p-toluenesulfonic acid (30 mg, 0.18 mmol) were added. The resulting reaction mixture was stirred at 50° C. for 6 h. After cooling to room temperature, water and toluene were added and the aqueous phase was extracted repeatedly with toluene. The combined organic phases were dried over magnesium sulfate, filtered and concentrated under reduced pressure. By column chromatography purification of the resulting crude product (ethyl acetate/heptane gradient), 2,3,7,9-tetramethyl-9-(trifluoromethyl)-1,4-dioxaspiro[4.5]dec-6-en-8-one (700 mg, 98% of theory) was obtained. In a round-bottom flask under argon, 2,3,7,9-tetramethyl-9-(trifluoromethyl)-1,4-dioxaspiro[4.5]dec-6-en-8-one (700 mg, 2.52 mmol) was then dissolved in abs. tetrahydrofuran (3 ml) and added dropwise to a solution of a lithium acetylide/ethylenediamine complex (376 mg, 3.27 mmol, 80% pure) in abs. tetrahydrofuran (5 ml). On completion of addition, the reaction mixture was stirred at room temperature for 4 h, then water was added and the mixture was concentrated under reduced pressure. The remaining residue was admixed with water and dichloromethane, and the aqueous phase was extracted repeatedly with dichloromethane. The combined organic phases were dried over magnesium sulfate, filtered and concentrated under reduced pressure. By column chromatography purification of the crude product obtained (ethyl acetate/heptane gradient), 8-ethynyl-2,3,7,9-tetramethyl-9-(trifluoromethyl)-1,4-dioxaspiro[4.5]dec-6-en-8-ol (550 mg, 68% of theory) was isolated as a colorless solid. Subsequently, copper(I) iodide (16 mg, 0.09 mmol) and bis(triphenylphosphine)palladium(II)chlorid (45 mg, 0.06 mmol) were initially charged under argon in a baked-out round-bottom flask, and abs. toluene (3 ml) and ethyl (2Z)-4,4,4-trifluoro-3-iodobut-2-enoate (126 mg, 0.43 mmol) were added. Stirring at room temperature for 10 min was followed by the dropwise addition of a solution of 8-ethynyl-2,3,7,9-tetramethyl-9-(trifluoromethyl)-1,4-dioxaspiro[4.5]dec-6-en-8-ol (130 mg, 0.43 mmol) in abs. toluene (1 ml) and of diisopropylamine (0.12 ml, 0.85 mmol). The resulting reaction mixture was stirred at room temperature for 3 h and then water was added. The aqueous phase was extracted repeatedly with dichloromethane. The combined organic phases were dried over magnesium sulfate, filtered and concentrated under reduced pressure. By final column chromatography purification of the crude product obtained (using an ethyl acetate/heptane gradient), ethyl (2E)-5-[8-hydroxy-2,3,7,9-tetramethyl-9-(trifluoromethyl)-1,4-dioxa-spiro[4.5]dec-6-en-8-yl]-3-(trifluoromethyl)pent-2-en-4-ynoate (110 mg, 52% of theory) was isolated in the form of a colorless oil. 1H-NMR (400 MHz, CDCl3 δ, ppm) 6.65/6.63 (s, 1H), 5.54/5.51/5.29 (s, 1H), 4.28/3.96 (q, 2H), 4.27/3.60 (m, 2H), 2.62 (br. s, 1H, OH), 2.47/2.34 (d, 1H), 2.01/1.99 (s, 3H), 1.98/1.91 (d, 1H), 1.42 (s, 3H), 1.31 (t, 3H), 1.28 (m, 3H), 1.17 (m, 3H).

1. customThe resulting reaction mixture
2. stirringthe mixture was stirred vigorously for 5 minutes
3. extractionthe aqueous phase was extracted repeatedly with dichloromethane
4. dry with materialThe combined organic phases were dried over magnesium sulfate
5. filtrationfiltered
6. concentrationconcentrated under reduced pressure
7. customBy column chromatography purification of the resulting crude product (ethyl acetate/heptane gradient), it